ROBERT SIEGEL, HOST:
From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel. On five occasions since 1990, the United Nations assembled a panel of scientists and asked for their best estimate of the risks and rate of global warming. Today, the latest incarnation of that panel met in Stockholm and released some of its conclusions. As NPR's Richard Harris reports, it finds once again that changes to the planet are picking up pace and that people are largely responsible.
RICHARD HARRIS, BYLINE: If you're in the construction business, you want an engineer's stamp on your blueprints to certify that someone has checked all the numbers. If you're a government wondering what to make of climate change, the equivalent of that official stamp comes from the Intergovernmental Panel on Climate Change. Chairman Rajendra Pachauri helped deliver the news this morning, global warming is already well underway.
RAJENDRA PACHAURI: Many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed. The amounts of snow and ice have diminished. Sea level has risen. And the concentrations of greenhouse gases have increased.
HARRIS: That echoes previous reports, but the IPCC did have some explaining to do because global air temperatures haven't increased for the past 15 years. The IPCC can't fully account for this in its report, but science panel co-chair Thomas Stocker says a big part of this could be that a Pacific Ocean weather pattern has ended up shunting a huge amount of heat into the deep ocean instead of leaving it in the atmosphere.
THOMAS STOCKER: That doesn't mean that the ocean saves us from global warming. It means that there would be much more powerful warming did we not have the ocean.
HARRIS: The IPCC scientists expect that's a temporary phenomenon, and eventually air temperature will continue on its long-term upward trend, though the worst-case scenario has been ratcheted back a bit. The forecast for sea level is it's likely to go up a foot or two this century, possibly a bit more, and that's somewhat worse than the estimate from the previous report.
IPCC author and Oxford University professor Myles Allen says it's no surprise to hear once again that the climate is changing and humans are largely responsible.
MYLES ALLEN: That said, there are some very important new elements brought out in this report. One of the key ones is the proposal for the first time of a cumulative carbon budget, that is the - an estimate of the total amount of carbon we can afford to dump in the atmosphere before pushing temperatures irrevocably above two degrees.
HARRIS: Two degrees Celsius is the internationally agreed upon goal to limit global warming. And scientists are fairly confident we'll reach that limit once another trillion tons of carbon are poured into the atmosphere. That could easily happen in this century. So the IPCC suggests government should track that figure with an eye toward curtailing all future emissions before we hit that number.
ALLEN: That really focuses the climate challenge and it presents governments with a very clear idea of what they need to do in order to stop climate change.
HARRIS: But unless there's a way to capture carbon as fossil fuels are burned, the only other option would be to leave a large share of oil, gas and coal reserves buried in the ground. And while that makes sense to scientists, it's a tough sell for governments, businesses and people who want to spend as little as possible for energy. Richard Harris, NPR News. Transcript provided by NPR, Copyright NPR.